Some people use these pans to melt and cast lead fishing weights and/or bullets.

That, and hobbyist bullet reloaders would use these to melt lead to cast into cheap bullets. Once you melt lead in the pan it will never be food safe again, I’d go as far as to drill a hole into the bottom so no one tries.

Metal salts are often water soluble, but a characteristic of lead salts is that they are especially water soluble. So heating up the pan with water should get rid of most of it. Boil water, pour it off, repeat a couple of times. If you're worried, use acidic water - it's going to mess up your pan but you've already proven that you know how to fix that, sir.

If you're curious, you can test for lead by doing the following first. Use distilled water and instead of boiling it, heat it to about 70 C. Keep it there for a couple of minutes while stirring gently. That should get most of the lead, if there is any, into the aqueous phase, while leaving behind any other metal salts that could theoretically be present.

Pour off the water into a different container. Let it cool down.

Take a portion of it to a borosilicate vial and a few drops of HCl (hydrochloric acid). If a white precipitate is formed, it may indicate lead. Together with the fact that your cations were soluble in hot water, the evidence is quite strong.

If you really want to be sure and want to do some real cation analysis, this page has a flowchart which, if you follow it, will let you know which oxidative state your lead was in and therefore help you infer what anion you have. I'd skip that part unless you want to do it for the sake of whimsy.